1. Field of the Invention
This invention relates to RF coupling devices and in particular to rectangular waveguides adapted for combination as cross-guide couplers.
2. Description of the Prior Art
Cross-guide couplers, as commonly constructed, each comprise two rectangular waveguides disposed at right angles with a coupling wall of each mated with that of the other to provide a common wall section through which electromagnetic energy is coupled between the waveguides. Typically, one or more coupling apertures are formed in the common wall section of one waveguide and an opening is formed in the other waveguide by entirely removing the common wall section thereof. The waveguide with the coupling aperture is then inset into the other waveguide such that the coupling walls of the two waveguides are coplanar, resulting in a single wall thickness through which energy is coupled.
The above described arrangement minimizes the effective wall thickness between waveguides thus optimizing coupling. Removal of the wall section causes problems, however, relating to the assembly and sealing of the couplers. For example, during assembly the waveguides must be properly aligned so that the coupling aperture in the one waveguide is properly located with respect to the opening in the other waveguide, and this often requires the construction of a special alignment fixture. After assembly the waveguides must be further processed to electrically and mechanically seal a hairline gap between the periphery of the opening in the one waveguide and the outer surface of the other. Typically, such sealing is accomplished by using a dip brazing or an oven brazing process. These processes are satisfactory for many applications, but have disadvantages. The size of waveguide assemblies that can be so processed is limited by the size of the brazing bath or the oven. Also, the temperature to which the assemblies are heated during the brazing process causes substantial expansion of the waveguides themselves, and waveguide distortion resulting therefrom may be unacceptably large if the waveguides are used in certain applications such as precision phased arrays or frequency scanned arrays.